Existing universal battery packs typically use a range of interchangeable external dc plugs, keys or output cables to select the desired output voltage for use with a range of portable electronic devices. The output voltage selection is based on the resistor value (or open/short pins) located within the external dc plug, key or output cable of each universal battery pack.
With the dc plug, key or output cable connected, the embedded resistor (or opens/shorts) connects directly or indirectly to the output dc-dc converter feedback path of the universal battery pack to select the desired output voltage. The output current limit of the universal battery pack is either fixed by the output dc-dc converter feedback path design or set by other embedded resistors within the same or another dc plug, key or output cable.
With typical designs such as that mentioned above, some problems may arise with usage of such typical universal battery packs. These problems include:
To support a wide range of portable electronic devices, users typically require a wide range of customised dc plugs, keys or output cables with one or more predetermined resistor values or open/short pins. Therefore, users are more prone to selecting a wrong dc plug, key or output cable.
In order to ensure that the correct dc plug, key or output cable is used to select a particular output voltage, the universal battery packs typically each require an additional plug, key or output cable with a pre-determined resistor value located within as a reference for voltage comparison. This presents a problem as an additional plug, key or output cable is required for use with each typical universal battery pack.
Another problem may be that universal battery packs utilising this typical design are typically prone to noise pick-up and error as the feedback path of an output dc-dc converter may be typically sensitive and especially so if the resistors or open/shorts are situated far away within the feedback path from the output dc-dc converter due to the length of the output cable. Noise pick-up and error may impact system performance and reliability.
Another problem with typical battery packs may be that manufacturers of such external battery packs may also typically include an ac adapter with each battery pack. This is because the battery pack design may not be suitable for use with a variety of ac adapters of different power requirements. The user may therefore be required to carry multiple ac adapters to power multiple portable electronic devices.